2-Butenedioic acid (HO2C–CH═CH–CO2H) exists as both cis (maleic) and trans (fumaric)…
CHEMISTRY · Multi-part · A Level · Chemistry · Introduction to organic chemistry · Introduction to organic chemistry
Problem
2-Butenedioic acid (HO2C–CH═CH–CO2H) exists as both cis (maleic) and trans (fumaric) geometric isomers depending on the relative positions of the two carboxyl groups about the C═C bond.
(a) For a single molecule of 2-butenedioic acid, determine the total number of σ bonds and the total number of π bonds.
(b) Explain why rotation about the central C═C bond does not occur under normal conditions and how this restriction leads to the existence of distinct cis and trans isomers.
(c) Propose one macroscopic physical property (e.g., solubility, melting point, or boiling point) that could be measured to distinguish experimentally between the cis and trans isomers. Justify your choice by relating the property to molecular structure and intermolecular interactions.